Cotton Bayou in Orange Beach is highlighted in this aerial photo. In response to residents' concerns over water quality in Cotton Bayou, possibly as a result of the 2010 Deepwater Horizon oil spill, the Orange Beach City Council voted on Tuesday, Nov. 20, 2012, to extend a contract with Auburn University to conduct a study of that specific backbay area. (Courtesy of city of Orange Beach)

ORANGE BEACH, Alabama -- It’s been nearly 2½ years since oil from the Deepwater Horizon disaster made its way through Perdido Pass into the city’s backbays and while time has diminished the visibility of the crude into tarballs, some residents of Cotton Bayou say they’re noticing a degradation of water quality.

The city has listened to residents’ concerns and on Tuesday the council approved a resolution allowing Auburn University researchers to extend a sediment and water-testing contract, which began in February 2011, to December 2014. The new testing will provide a thorough assessment of the Cotton Bayou area, west of Perdido Pass, to the tune of $30,000, all of which is covered by an existing BP grant.

“Back in 2010 and 2011 we were taking sample from all over town -- backbays, Gulf front, Terry Cove, Cotton Bayou, etc., to determine if there were any impacts from Corexit, whatever dispersants, or MC252 oil,” Phillip West, coastal resource manager for Orange Beach, said of the oil from Mississippi Canyon Block 252 that the Deepwater Horizon rig tapped into. “The Cotton Bayou study somewhat stems from residents’ concerns that Cotton Bayou has significantly degraded since the oil spill. Maybe some conditions have changed as a result of the oil spill and basically the study is going to give us the in-depth facts.”

Mayor Tony Kennon said the reason for the study is two-fold.

In the file photo from June 16, 2010, layers of boom are deployed at Perdido Pass in Orange Beach, Ala. Although many precautions were taken following the Deepwater Horizon accident in April 2010 some residents in backbay areas of Orange Beach are concern about the water quality. In response to those concerns, the Orange Beach City Council on Tuesday, Nov. 20, 2012, approved a study of Cotton Bayou to be conducted by Auburn University. (Mike Kittrell/mkittrell@al.com)

“Number one, we want to alleviate all residents’ concerns, post oil spill,” he said. “And number two, this is something that we need to be doing on a regular basis. Making sure that we don’t see an ongoing, insidious degradation of our water quality without us noticing or paying attention.”

Results from Auburn’s earlier studies of the city’s backbays, including Cotton Bayou, found that it was unlikely that traces of chemicals present in the water originated from dispersant, such as Corexit, used during the early stages of the oil spill response. According to the report, the chemicals found are common in household products and the concentrations found in the data "do not pose a risk to human and ecological health due to the low levels observed."

Since those early studies Auburn researchers have continued to assist the city in studying tarballs that wash ashore, especially during hurricanes and tropical events, as well as testing offshore borrow sites for the ongoing beach renourishment project. In a report released in September, an Auburn-conducted chemical analysis shows that tarballs and tar found stuck to shells and other small Gulf-bound material, are linked to the BP oil spill and are hundreds to thousands of times more common than the other tar deposits found on the beach.

Away from the Gulf-front property where the majority of tarballs are found after rough weather, residents in Cotton Bayou have other concerns, West said. Some say they’re seeing changes that have never happened before such as a decline in the population of blue crabs and a drop in fish, such as white trout.

West said the new study will be a fairly lengthy project but he expects to have some preliminary results ready for residents very soon. A full report will not be ready for about a year.

“We’ll be taking samples based on rain events, also based on just a point in time seasonally. It’s fairly elaborate, but not too much,” West said. “I mean $30,000 doesn’t buy you a tremendous amount of information but it is significant. I think we can use that to infer what may be going on as far as water quality. For example, if there isn’t a problem with MC252 oil or Corexit, what are the sources and how do we address them from the land side if they’re a land-based source. Is it nutrients? Is it fertilizers? Is it petroleum other than MC252? Maybe it’s roadway runoff. We just don’t know and this is going to help us take a closer look.”

West sees this latest study as a progression of research that will have to be done for many years to come in order to fully understand the oil spill’s impact.

“At some point I see us looking very closely at fish and plant tissue to see if there’s any accumulation there and we’ll probably contract with Auburn,” West said. “They have a proposal ready but it’s going to be a little more money than we have in our bank account from the BP block grant money.”

Follow Marc Anderson, Baldwin County community news reporter, on Twitter:@MarcD_Anderson